Minnesota soybean growers have been searching for solutions to combat the massively destructive soybean aphid and reduce insecticide use ever since the aphid was introduced to North America in the early 2000s. Aaron Lorenz, associate professor in the Department of Agronomy and Plant Genetics, is developing a solution to aphids that he hopes will drastically reduce the need for insecticide application in Minnesota as part of a research team led by Extension entomologist Robert Koch.

“I don’t know any farmers that want to spray insecticides,” said Lorenz.

Soybean varieties containing aphid resistant genes have been scarce in the Midwest, but are almost nonexistent here in the “Bold North.” Lorenz’s research focuses on the development of early-maturing, aphid-resistant lines that can withstand the northern climate of Minnesota.

Research roots

The earliest roots of this work trace all the way back to the 1890’s, with the start of a collection of soybean germplasm now known as the USDA Soybean Germplasm Collection.

“The collection became an important reservoir of genetic diversity that we can search through for resistance to new pests,” said Lorenz.

Researchers have been adding to it throughout the years. Some of the biggest and most valuable additions were added in the 1920s and 1930s by early soybean geneticists. These geneticists went on expeditions to East Asia where the soybean originated and collected different varieties grown by farmers there.

When the soybean aphid (Aphis glycines) first invaded North America, soybean breeders were able to screen thousands of existing soybean varieties held in the USDA Collection in search of any that had some level of resistance to the aphid. When a new pest or disease is introduced to the US, the Soybean Germplasm Collection is one of the first places researchers go in search of resistant varieties.

“The collection became an important reservoir of genetic diversity that we can search through for resistance to new pests.”

Lorenz and his team zeroed in on soybean lines in the collection that contained soybean aphid-resistance genes called Rag – 'resistant to Aphis glycines' – to serve as building blocks for aphid-resistant lines in Minnesota.

Through traditional breeding, Lorenz has been putting these genes to the test to come up with robust aphid resistant soybean lines that could reduce or eliminate insecticide application for soybean aphids in Minnesota fields.

Beating the soybean aphid

Building off the work of his predecessor Jim Orf, a professor emeritus in the Department of Agronomy and Plant Genetics, Lorenz has already commercialized one soybean variety with soybean aphid resistance with Viking Seeds based in Albert Lea, Minnesota (Viking 0.0654AT). At least nine additional lines are in advanced stages of testing. Results expected in late winter of 2019 or spring of 2020 will determine whether these varieties perform well enough to be advanced.

Challenges can arise with a lone Rag gene in a resistant line, with the aphid quickly adapting to resistance in the plant. Plants are being bred to control the aphids while the aphids are continually adapting to these new plants, creating a complicated “arms race” between plants and aphids. The development of aphid resistance to overcome host-plant resistance is a real concern.

“The potential for resistance development to these lines is a huge challenge. I wouldn’t say it was unexpected, but it is definitely a challenge,” said Lorenz.

The solution to this issue may lie in the ‘stacking’ of multiple Rag genes to create a stronger, more robust resistance. Lorenz has confirmed and tested four different Rag genes: Rag1, Rag2, Rag3, and Rag4. Stacks containing all Rag genes would be the ideal, but varieties with Rag1 and Rag2 may confer enough protection against aphids if not used widely. As far as he knows, Lorenz says no known aphid would be able to overcome resistance to four stacked Rag genes. Stacking genes, however, is no easy feat.

“It takes a lot of work to go from these lines to a line that is built for seeds in Minnesota. If we can help bridge that gap, it is more likely that seed companies will pick it up and integrate soybean aphid resistance into their own seed mixes. ”

"We are interested in finding resistance genes wherever they occur. Rag1 was found in a soybean variety called 'Jackson,' which originated in the southeastern United States and was released in 1953. Others might be in soybean varieties originally bred for hay almost a century ago or still to be discovered in soybean land races from Asia. It takes a lot of work to go from these lines to a line that is built for seeds in Minnesota. If we can help bridge that gap, it is more likely that seed companies will pick it up and integrate soybean aphid resistance into their own seed mixes,” said Lorenz.

Lorenz’s team generally has to sort through double the number of individual plants with each desired resistance gene to create stacked varieties.

“If we want 250 new breeding lines that have resistance to four Rag genes, we really need to screen about 4000 breeding lines.”

Even though the numbers may be difficult to achieve, he believes all the work will pay off.

"We are confident that we can bring Rag genes, alone or in stacks, into varieties that are well suited for Minnesota. We are also keeping an eye out for new Rag genes, other genes for aphid resistance, or new ways to design resistance genes to control aphids that might develop resistance to our varieties." said Lorenz.

A win for everyone

Organic farmers have shown excitement over aphid resistant soybean lines, because synthetic insecticides have never been an option for them. With a goal to drastically reduce or even eliminate the need for chemical applications in soybean aphid controls, conventional farmers have shown similar excitement in also eliminating the cost of spraying.

Aside from cost, Lorenz is also concerned about making sure the lines produce competitive crop yield. A successful resistant line will achieve this as well as suppress the aphid population to below 250 insects per plant — a low number considering over 1000 aphids can easily take over just one soybean plant.

“It’s not necessarily about the cost. It’s making sure they yield as well as the commercial varieties that come from the big companies,” said Lorenz.

“We could develop lines that have resistance rather than spray insecticides, and it's good all the way around. It's good for a farmer's economic situation, it's good for the environment, it's good for human health.”

As the team continues their research, Lorenz hopes that the end product will consist of twice as many soybean varieties that have aphid resistance and good yield that are adapted to Minnesota and will become commercially available to growers.

“We could develop lines that have resistance rather than spray insecticides, and it’s good all the way around. It’s good for a farmer’s economic situation, it’s good for the environment, it’s good for human health,” said Lorenz.

Funding for this project was provided by the Environment and Natural Resources Trust Fund as recommended by the Legislative and Citizen Commission on Minnesota Resources.

About the Author

Maggie Nesbit is a Communications Intern with the Minnesota Invasive Terrestrial Plants and Pests Center (MITPPC). She is a double major in English and Strategic Communications at the University of Minnesota. In her spare time, Maggie enjoys running, hiking, reading and spending time with friends and family. Maggie's position is funded by a grant from the Minnesota Soybean Research & Promotion Council.